Carbonyl nickel powder

ABSTRACT

Nickel carbonyl is thermally decomposed to nickel powder or pellets in the presence of nitric oxide, nitrogen trioxide or nitrogen peroxide in concentrations of 1 - 5000 ppm. or more. By suitable choice of gas concentrations and temperatures in the range 230 - 350*C the powder can be produced with substantially spherical particles or with low carbon content or both.

D United States Patent 1191 1111 3,820,977 Llewelyn [4 June 28, 1974 CARBONYL NICKEL POWDER [56] References Cited [75] Inventor: David Myers Llewelyn, Swansea, UNITED STATES PATENTS W e 2,844,456 7/ 1958 Llewelyn et al 75/.5 AA Assignee: West et al- New York Primary Examiner-W. W. Stallard [22] Filed: Aug. 21, 1972 [21] Appl. No.: 282,570 ABSTRACT Nickel carbonyl is thermally decomposed to nickel '30] Foreign Application Priority Data powder or pellets in the presence of nitric oxide, nitro- J ly 7, 1970 Great Britain 32959/70 gen trioxide or nitrogen peroxide in concentrations of 1 5000 ppm. or more. By suitable choice of gas con- Related US, Application Dat centrations and temperatures in the range 230 [62] Division of Ser. No. 159,258, July 2, 1971, Pat. No. C the Powder can produced substantially 3,702,761- spherical particles or w1th low carbon content or both.

1 Claim 6 Drawin Fi ures 52 US. (:1. 75/.5 AA g g [51] Int. Cl

Field of Search 75/.5 AA

PATENTED I974 SHEET 1 BF 3 FIG.

PAIENTEEUumza m4 SHEET 2 OF 3 FIG.4

PATENTEDJUH28 1974 3,820,977

sum 3 or 3 1 CARBONYL NICKEL POWDER The present application is a division of my application Ser. No. 159,258 filed July 2, 1971, which is now U.S. Pat No. 3,702,761 issued Nov. 14, 1972.

The present invention relates to the production of metallic nickel and more particularly to the production of metallic nickel by the thermal decomposition of nickel carbonyl.

Nickel carbonyl has been decomposed in various ways. For example, nickel carbonyl is passed over nickel pellets heated above the decomposition temperature of the carbonyl to deposit nickel on the surface of the pellets so that they increase in size. Nickel carbonyl has also been decomposed in the hot free space of a decomposer to produce nickel powder having variously shaped particles according to the temperatures employed. Nickel carbonyl has also been decomposed on the surface of hot powder particles, which can be nickel or other materials, that are to be coated with nickel, in the form of a fluidized bed or a suspension of powder in the stream of carbonyl-containing gas.

One of the problems encountered in decomposing nickel carbonyl is contamination of the metal product, particularly nickel powder, with carbon. The carbon is produced by the disproportionation of carbon monoxide, and the amount produced increases with increasing temperatures. In U.S. Pat. No. 3,367,767, a process for decomposing nickel carbonyl in a steel reactor having nitrided walls and in the presence of controlled amounts of ammonia and oxygen to produce nickel powder with low carbon contents is disclosed. U.S. Pat. No.3,367,768 discloses a process for decomposing nickel carbonyl to spherical nickel powders by decomposing nickel carbonyl in the presence of controlled amounts of ammonia and oxygen to incorporate at least about 0.01% nitrogen in the powder to insure that the powder assumes a spherical shape. These processes work reasonably well, but in practice the off-gases, primarily carbon monoxide, must be treated to separate the ammonia and oxygen from the carbon monoxide. Although attempts have been made to avoid the foregoing problems, none, as far as I am aware was entirely successful when carried into practice commercially on an industrial scale.

It has now been discovered that nickel carbonyl can be decomposed to metallic nickel having low carbon contents at increased rates by adding special oxides of nitrogen to the decomposer. If added in sufficient quantities the special oxides of nitrogen are also effective in producing spherical nickel powder.

An object of the present invention is to provide spherical carbonyl nickel powder having smooth surfaces.

Other objects and advantages will become apparent from the following description taken in conjunction with the accompanying figures in which:

FIGS. 1 to 4 are representations of photomicrographs of carbonyl nickel powder having increasing nitrogen contents from FIG. 1 to FIG. 4 taken by transmitted light at a magnification of 1,000 times;

FIG. 5 is a scanning electron micrograph of prior art spherical carbonyl nickel powder at a magnification of 10,000 times, and

FIG. 6 is a scanning electron micrograph of spherical carbonyl nickel powder in accordance with the present invention at a magnification of 10,000 times.

Generally speaking, the present invention is directed to spherical carbonyl nickel powder containing at least about 0.01% nitrogen and having substantially smooth surfaces when microscopically examined at a magnification of 10,000 times.

The present invention is based on the discovery that the rate of thermal decomposition of nickel carbonyl under otherwise similar conditions of temperature and carbonyl concentration is increased by the presence of at least one nitrogen oxide selected from the group consisting of nitric oxide (NO), nitrogen trioxide (N 0 or nitrogen peroxide (N0 and according to the present invention nickel is produced by the thermal decomposition of nickel carbonyl in the presence of one of these gases.

The amount of the oxides of nitrogen employed can vary widely, and these gases have been found to be effective in concentrations ranging from 1 to 1,000 parts per million of the carbonyl-containing gases. Even higher concentrations can be used, but the presence of the oxide of nitrogen during the decomposition introduces nitrogen into the nickel produced, and as the concentration increases so does the nitrogen content of the product. Very high concentrations, e.g. up to 2,000 or 3,000 or even 5,000 ppm, can therefore only be employed when relatively high nitrogen contents in spherical powders can be tolerated.

It should be noted that all gaseous compositions or additions are given on a volumetric basis unless otherwise stated while solid compositions are given on a weight basis.

The use of nitrogen oxideswill now be described in more detail in relation to the production of carbonyl nickel powder, that is to say powder made by the thermal decomposition of nickel carbonyl vapour in the hot free space of a decomposer.

When nitric oxide, nitrogen peroxide or nitrogen trioxide is used in place of ammonia or ammonia and oxygen as described in U.S. Pat. No- 3,367,767, it is found that powder consisting of discrete particles can be produced at an increased rate in a vessel of given size. The optimum conditions vary with the properties required in the powder, but broadly for the production of powder of given properties the temperature (and therefore the rate) of decomposition can be higher than when ammonia and oxygen are added, and, moreover, the concentration of oxide of nitrogen required is less than that of ammonia.

It is advantageous to use nitric oxide, which is more effective than the other two oxides. To achieve equivalent results greater amounts of nitrogen trioxide or nitrogen peroxide are required than when nitric oxide is employed.

The production of powder can be carried on in the temperature range of 230 to 350C. Below 230C so small a proportion of the carbonyl is decomposed to powder that the process is not practicable on an industrial scale. Above 350C a high proportion of filamentary aggregates are formed. A very suitable temperature is 290C.

The amount of oxide of nitrogen required varies with the temperature, decreasing as the temperature decreases. Considering nitric oxide, and assuming that low carbon content is required, some reduction in the carbon content is obtained with very small amounts of nitric oxide, that is to say, as little as 1 part per million, particularly if the vessel walls have previously been. ni-

trided and the process is operated continuously. When a steel reactor is employed, the walls of the reactor can be initially nitrided by introducing ammonia into the reactor and heating the reactor to nitriding temperatures, e.g., 500C, for at least 1 hour, e.g., 3 hours. It is found that as the concentration of nitric oxide increases, the carbon content falls and then rises again. Typically the nickel carbonyl is introduced into the decomposer, as a gas mixture of carbon monoxides containing 8% nickel carbonyl, and at this concentration and at 290C the concentration of nitric oxide should be from 50 ppm to 200 ppm. Above 250 ppm the carbon content of the powder can actually be higher than if no nitric oxide is added.

Converted into percentage of the carbonyl by volume, at 290C the nitric oxide should be from about 0.06% to about 0.25% of the carbonyl, whatever the concentration of the carbonyl.

In controlling the carbon content of the carbonyl nickel powder, at lower temperatures the nitrogen oxide concentration in the gaseous mixture is correspondingly lowered, being from 25 to 100 ppm, i.e. 0.03 to 0.12%, at 230C, and at higher temperatures it is correspondingly increased, being from 100 to 300 ppm, i.e. 0.12 to 0.4% at 320C.

When the object is to produce spherical powder, the concentration of nitric oxide at 290C should be at least 0.09% of that of the carbonyl. If the temperature is lower, this minimum can be correspondingly reduced, but at 230C should be at least 0.012%. Likewise at higher temperatures the minimum concentration of nitric oxide must be'higher, being at least 0.2% at 320C.

If low carbon content is not important, the concentration of nitric oxide can be considerably higher, but so far as the production of spherical powder is concerned there is no advantage in exceeding 1.25 or even 0.625% of the carbonyl concentration.

It is clear that the shape of the powder depends on the incorporation of nitrogen into the powder, but the mechanism by which this occurs is unclear. Whatever the mechanism is, nitrogen peroxide is less effective than nitric oxide, and nitrogen trioxide is still less effective. It is therefore necessary-to use increased quantities of these gases in order to obtain results equivalent to those obtained with nitric oxide.

The way in which the process can be controlled to produce powders of different properties is shown by the results of a large number of tests. All these were carried out in an externally heated decomposer havmg a diameter of 10 inches and mild steel walls, which are p nitrided as a result of use in numerous processes in which ammonia has been added. In all the tests carbon monoxide gas containing from 7 to 9% of nickel carbonyl was fed into the decomposer through an inlet at the top at a rate (unless otherwise stated) of 2,000 litres per hour. The oxide of nitrogen, when used, was injected into the gas stream at a measured rate at room temperature. The temperature at the inlet to the decomposer was maintained at about 50C by water coolmg.

The particles obtained varied in shape as shown in the accompanying Figures, and were classified as follows:

FIG. 1 spiky FIG. 2 angular, the spikes becoming rounded FIG. 3 nearly spherical FIG. 4 spherical Spherical powder made by the process of the invention has also been examined using the scanning electron microscope at a magnification of X 5000 and X 10000 and it is surprisingly found that the surface of these powders is smoother than powders made by the use of ammonia and oxygen which have a similar appearance under the optical microscope. The difference in surface characteristics of spherical carbonyl nickel powder produced by decomposing nickel carbonyl in the presence of ammonia and oxygen, as taught in US. Pat. No. 3,367,768, and in the presence of nitric oxide is shown in FIGS. 5 and 6. FIG. 6 dramatically confirms that spherical carbonyl nickel powder produced by de composing nickel carbonyl in the presence of nitric oxide and containing at least about 0.01% nitrogen has smooth surfaces as compared with the rough surface of spherical carbonyl nickel powder produced by decom-,

posing nickel carbonyl in the presence of ammonia and oxygen.

In the first set of tests the decomposer temperature was maintained at 290C, nitric oxide was used and the concentration of the nitric oxide was varied. Table I below shows the concentration of the carbonyl by volume, the amount of nitric oxide introduced (in parts per million), the particle size of the powder as measured in the Fisher apparatus, the bulk density of the powder, the carbon and nitrogen contents of the powder and the particle shape. The first three tests, A, B and C, are given by way of comparison. Test A, which is in fact the test numbered 1 in US. Pat. No. 3,367,767, and Test B were carried out in the decomposer before its walls were nitrided. Test C was carried out at a time when the walls of the decomposer were nitrided.

TABLE I Test Carb. Nitric Fishcr Bulk Chemical Particle Concn. Oxide Value Density Character- Shape /r p.p.m. Microns gms./cc istics A 9.0 4.47 2.47 .057 .001 Spiky C 8.0 4.37 2.41 .029 do. do. B 7.0 3.66 1.99 .039 do. do. 1 8.5 1,000 4.96 3.21 .069 .17 Spherical 2 8.5 500 5.25 3.23 .056 .08 do. 3 8.5 250 5.95 3.71 .023 .024 do. 4 8.0 5.76 3.60 .022 .014 do. 5 8.0 62 6.73 3.29 .017 .008 Nearly Spherical (1 8.0 31 6.74 3.03 .020 .005 Angular and Irregular 3 ,8 20,977 5 6 This table shows an optimum concentration of nitric increasing the rate of gas flow is shown by two further oxide to be 62 ppm at 290C and nickel carbonyl contests, reported in Table IV below, in which Test 7 is recentrations between 8 and 8.5% when powder of low produced by way of comparison and a further expericarbon content is required. It also shows that, as when ment (D) carried out in the nitrided decomposer but in ammonia and oxygen are added, a minimum of 0.01% 5 the absence of nitric oxide is also reported TABLE IV Test Dec. Gas Carbonyl Nitric Fisher Bulk 7r 7: Ni

Temp. Flow Concentr- Oxide Value Density C N in C M lhr ation (72) ppm. Microns gms/cc outlet gas D 320 2 8.5 2.75 1.67 .048 .0Oi Nil 7 320 2 8.0 62 4.43 2.66 .032 .006 Nil [3 320 3 8.5 62 3.8 2.26 .035 .006 llflCC I4 320 4 3.5 62 4.69 2.67 .027 .008 trace nitrogen is required in the powder to produce a spheri- I Table IV shows that the addition of nitric oxide alcal particle shape. ways increases the particle size and bulk density, lowers In the next series of tests a nitric oxide concentration the carbon content and introduces a small amount of of 62.5 ppm was maintained and the decomposer tem- 2O nitrogen into the powder, and that, despite doubling perature was varied, with the following results: the gas flow rate for tests 13 and 14, the powder char- TABLE II Test Dec. Curb. Fisher Bulk Chemical Powder Temp. Concn. Value Density Character- Shape C 7'; Microns gms./cc. istics 7 320 8.0 4.43 2.66 .032 .006 Angular 5 290 8.0 6.73 3.29 .017 .008 Nearly Spherical 8 260 8.5 7.30 3.11 .018 .01 1 Spherical 9 230 9.0 9.02 3.75 .014 .038 Spherical In the next series of tests the concentration o f nitric aeteri ties were maintained, particularly the low can oxide was increased to 125 ppm, and the decomposer b content,

temper ture w gain ri h h f llo ng r Test D demonstrates how inthe absence of nitric sults: oxide bulk densities were low, and in fact the powder TABLE III Test Dec. Carb. Fisher Bulk Chemical Powder Temp. Concn. Value Density Character Shape C 71 Microns gms/cc. istics 10 320 9.0 4.56 2.86 .021 .008 Angular 4 290 8.0 5.76 3.60 .022 .014 Spherical Tables II and III clearly indicate that the highest nihad some B Type characteristics.

triding efficiency, leading to spherical particles and low Finally Table V shows comparative results obtained carbon contents, is obtained at low decomposer temwith the same oxides of nitrogen under identical condiperatures. Further, the particle shape can be modified tions, namely a decomposer temperature of 260C and by varying the decomposer temperature while maina concentration of the oxide of nitrogen that equalled taining a constant addition of nitric oxide. 1.25% by volume of the carbonyl.

Test 7 shows that even at high decomposition tem- TABLE V peratures, powders of low carbon content can be produced with the normal particle size and bulk density of Test A 3 5 i We Value Density C N Type A powder (discrete, angular particles). In con- Microns gmsjcc. trast, with optimum ammonia and oxygen concentration (2,000 ppm ammonia and 1,500 ppm oxygen) :2 $8 12% :5; 8%? under the same conditions of temperature, rate of gas 17 1 1 I flow and carbonyl concentration Type B powder (agglomerates of interlocking spiky filaments) containing Although the present invention has been described in 0.12% carbon was produced. conjunction with the production of nickel powder, it

In all the tests (except A and B) the free carbon conmay also be used in the production of nickel pellets, for

tent of the powders was negligible. Even at high inlet which the decomposition temperature will generally be concentrations nitric oxide was not detected in the outless than 230C, e.g. I 220C.

let gas by chromatograph. It is to be understood that other modifications and The advantage that the output can be increased by variations may also be resorted to without departing from the spirit and scope of the invention, as those 1. Spherical carbonyl nickel powder containing at skilled in the art will readily understand. Such modifileast about it g n and having substantially cations and variations are considered to be within the Smooth Surfaces when microscopically examined at a purview and scope of the invention and appended clai magnification of 10,000 times.

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